Fmcw radar reduced power mode

ABSTRACT

A method of operating a frequency modulated continuous wave (FMCW) radar system includes receiving, by at least one processor, digital intermediate frequency (IF) signals from a mixer coupled to a receive antenna. The method also includes computing, by the at least one processor, a motion metric based on the digital IF signals; operating, by the at least one processor, the FMCW radar system in a classification mode, in response to determining that the motion metric is above a threshold; and operating, by the at least one processor, the FMCW radar system in a detection mode, in response to determining that the motion metric is below the threshold for at least a first amount of time. An amount of power consumed by the FMCW radar system in the detection mode is less than an amount of power consumed by the FMCW radar system in the classification mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/173,795, filed Oct. 29, 2018, which is incorporated by referenceherein in its entirety.

SUMMARY

In accordance with at least one example of the disclosure, a method ofoperating a frequency modulated continuous wave (FMCW) radar systemincludes receiving, by at least one processor, digital intermediatefrequency (IF) signals from a mixer coupled to a receive antenna. Themethod also includes computing, by the at least one processor, a motionmetric based on the digital IF signals; operating, by the at least oneprocessor, the FMCW radar system in a classification mode, in responseto determining that the motion metric is above a threshold; andoperating, by the at least one processor, the FMCW radar system in adetection mode, in response to determining that the motion metric isbelow the threshold for at least a first amount of time. An amount ofpower consumed by the FMCW radar system in the detection mode is lessthan an amount of power consumed by the FMCW radar system in theclassification mode.

In accordance with another example of the disclosure, a frequencymodulated continuous wave (FMCW) radar system includes a receive antennaand a receive channel coupled to the receive antenna. The receivechannel is configured to generate a digital intermediate frequency (IF)signal from a radio frequency signal received by the receive antenna.The FMCW radar system also includes a processor coupled to the receivechannel. The processor is configured to compute a motion metric based onthe digital IF signals; operate the FMCW radar system in aclassification mode, in response to determining that the motion metricis above a threshold; and operate the FMCW radar system in a detectionmode, in response to determining that the motion metric is below thethreshold for at least a first amount of time. An amount of powerconsumed by the FMCW radar system in the detection mode is less than anamount of power consumed by the FMCW radar system in the classificationmode.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a block diagram of a frequency-modulated continuous wave(FMCW) radar system in accordance with various examples;

FIG. 2 shows a range-Doppler array in accordance with various examples;

FIGS. 3a and 3b show FMCW radar frames in a detection mode and aclassification mode in accordance with various examples;

FIGS. 4a and 4b show flow charts of methods for operating a FMCW radarsystem in accordance with various examples;

FIG. 5 shows a range-Doppler array for computing a motion metric inaccordance with various examples; and

FIG. 6 shows a block diagram of a FMCW radar system including a FMCWradar system-on-a-chip (SOC) in accordance with various examples.

DETAILED DESCRIPTION

Frequency-modulated continuous wave (FMCW) radar systems may be embeddedin multiple usage applications, such as industrial applications,automotive applications, and the like. As the cost of FMCW radartransceiver integrated circuits (ICs) becomes lower over time, FMCWradar systems are increasingly suitable for gesture recognitionapplications, such as controlling devices around the home (e.g., athermostat, lighting for a room), controlling personal electronicdevices (e.g., a mobile phone), or control of automotive subsystems(e.g., temperature regulation, audio systems, navigation systems).

FMCW radar systems may transmit a frame containing a series of frequencyramps referred to as chirps. These chirps may be reflected by an objectback to the FMCW radar system. After receipt of a signal containing thereflected chirps, the FMCW radar system may down-convert, digitize, andprocess the received signal to determine characteristics of the object.These characteristics can include range, velocity, angle of arrival,etc., of the object when the object is in view of the FMCW radar system.

In at least some FMCW radar systems, multiple sequences of chirps (e.g.,such as consecutive sequences of equally spaced chirps) are transmittedand reflections of these chirps received to generate radar signals.After each sequence of chirps, there may be some idle time (e.g.,inter-frame idle time) to allow for processing the radar signalsresulting from the reflected chirps. The acquisition time of a sequenceof chirps and the subsequent inter-frame idle time together may form aradar frame. In at least one example, the reflected signal received byeach antenna of the FMCW radar system is mixed with the transmittedsignal to generate an intermediate frequency (IF) signal that isfiltered and digitized. Signal processing may then be performed on theresulting digital IF signals (e.g., one per receiving antenna in theFMCW radar system) to extract any one or more of the range, velocity,and/or angle of potential objects in the view of the radar.

Effectively recognizing and categorizing gestures benefits from a FMCWradar system with several characteristics. First, sufficiently highvelocity resolution provides the ability to detect fine movements, whichrequires a long frame time. Second, sufficiently high chirp bandwidthprovides good range resolution, which requires a longer chirp duration.Third, a relatively high maximum detectable velocity provides theability to capture faster-moving gestures, which requires a smaller timebetween chirps. Fourth, sufficiently high angle resolution provides theability to capture high levels of spatial detail associated withgestures, for example by transmitting chirps/frames from multipletransmit antennas. Finally, a fast update rate provides the ability tocapture or sample the relevant dynamics of a fast-moving gesture, whichrequires frames to be closely spaced (or have a minimal inter-frame idletime). The foregoing requirements, which may be referred to asattributes of operation of the FMCW radar system, have the effect ofincreasing power consumption of the FMCW radar system as well ascreating potential thermal management issues, both of which areundesirable.

In examples of the present disclosure, a FMCW radar system is configuredto operate in either a detection mode or a classification mode. While indetection mode, certain attributes of operation of the FMCW radar systemare tailored to reduce power consumption, while still being able todetect movement of object(s) in the field of view of the FMCW radarsystem that could be gestures. For example, the maximum detectablevelocity and angle resolution are of a lower priority since no actualgesture classification is being performed. As a result, in detectionmode, only a single transmit antenna may be used since angle resolutionis a lower priority. Further, in detection mode, the time between chirpsmay be increased since the maximum detectable velocity is a lowerpriority.

On the other hand, while in the classification mode, certain attributesof operation of the FMCW radar system are tailored to classify gestures,which, unlike merely detecting movement of object(s) that could begestures, may require that maximum measureable velocity and angleresolution be of a higher priority. Thus, in classification mode,multiple transmit antennas may be used to improve angle resolution.Further, in classification mode, the time between chirps may bedecreased relative to detection mode to improve the maximum detectablevelocity.

In certain examples, the FMCW radar system is additionally configured tooperate in standby mode, where a slower response time is tolerable, andthus the update rate may be deprioritized. As a result, in standby mode,the inter-frame idle time may be increased, further reducing powerconsumption.

To determine whether to operate in standby mode, detection mode, orclassification mode, the FMCW radar system is configured to compute amotion metric based on detected objects and motion of the detectedobjects (e.g., velocity of the detected objects). As a result of themotion metric rising above a threshold, which indicates detected motionthat could be a gesture, the FMCW radar system is configured to operatein classification mode. As a result of the motion metric falling belowthe threshold for at least a predetermined amount of time, the FMCWradar system is configured to operate in detection mode (or, in someexamples, standby mode). In some examples then, power consumption of theFMCW radar system is reduced in detection mode when gestures are notbeing performed, while the FMCW radar system retains the ability toswitch modes of operation to classification mode to classify orrecognize a gesture by a user. Similarly, power consumption of the FMCWradar system is further reduced in standby mode, while the FMCW radarsystem retains the ability to switch modes of operation toclassification mode to classify or recognize a gesture by a user.

FIG. 1 shows a block diagram of an example FMCW radar system 100. TheFMCW radar system 100 includes a transmit antenna 102 and a receiveantenna 104. In the FMCW radar system 100, a local oscillator 108generates frequency ramps, referred to as chirps, which are transmittedby the transmit antenna 102. For example, the local oscillator 108comprises a voltage controlled oscillator (VCO) and the chirps aregenerated by linearly ramping a control voltage supplied to the VCO. Thechirps are also provided to a mixer 110, which is coupled to the localoscillator 108. In at least one example, the FMCW radar system 100transmits a 4 GHz bandwidth chirp that ramps from 77 GHz to 81 GHz.Multiple chirps are transmitted sequentially in a frame.

The transmitted radar signals are reflected and received by the receiveantenna 104. The received radio frequency (RF) signals are mixed withchirps from the local oscillator 108 by a mixer 110 in a receive channel114, to generate intermediate frequency (IF) signals. IF signals arealso referred to as dechirped signals, beat signals, or raw radarsignals. An analog-to-digital converter (ADC) 116 in the receive channel114 digitizes the IF signals. The digital IF signals are sent by the ADC116 to a digital signal processor (DSP) 118 for further processing. TheDSP 118 may perform signal processing on the digital IF signals toextract the range and velocity of objects in view of the FMCW radarsystem 100. Range refers to the distance of an object from the FMCWradar system 100 and velocity refers to the speed of the object relativeto the FMCW radar system 100.

To determine the range, the DSP 118 performs a range fast Fouriertransform (FFT) on the digital IF signals corresponding to each chirp ina frame of chirps, to convert the data to the frequency domain. For eachof M time samples in a chirp, the DSP 118 computes a range FFT, whichyields M range results for the chirp. Thus, for a frame having N chirps,the range FFT generates a range-time array having NxM range values. Inthe range-time array, the M columns indicate the range values forsamples at the same relative time across the N chirps.

To determine the velocity, the DSP 118 performs a Doppler FFT over therange values of the chirps in the frame, which generates a range-Dopplerarray. That is, the Doppler FFT is performed on each of the M columns ofthe NxM range-time array. The peaks in the NxM range-Doppler arraycorrespond to the range and relative speed or velocity of objects. Thecombination of the range FFTs and the Doppler FFTs may be referred to asa two-dimensional (2D) FFT (or 2D FFT processing).

FIG. 2 shows a result (range-Doppler array 200) of the 2D FFT processingon a frame of chirps, which resolves a scene into a 2D grid with rangeand velocity on the two axes. The cells in this grid are commonlyreferred to as bins. A peak 202 in a curve in the 2D grid indicates anobject in the scene. The coordinates of such a peak 202 in the curve inthe range-velocity plane indicate the range and velocity of the object.The DSP 118 or other processor performs an object detection algorithm todetect peaks 202 in the 2D FFT grids. Additionally, the DSP 118 maytrack the detected objects across frames.

Multiple objects with the same range and relative velocity with respectto the FMCW radar system 100, but at different angles, may be placed inthe same bin in the 2D grid. In some examples, two or more transmitantennas generate chirps that are interleaved within a frame todiscriminate multiple objects in the same bin by determining the angleof the objects. In other examples, two or more receive antennas may beused to discriminate multiple objects in the same bin by determining theangle of the objects. The use of multiple transmit and/or multiplereceive antennas improves the angle resolution capability of the radarsystem. A third FFT, an angle FFT, is performed across the 2D FFT grids(one 2D FFT grid being computed for each transmit-receive antenna pair),to determine the angles for the objects. Accordingly, objects withsimilar range and velocity, but different angles are resolved. The anglemay be the azimuth angle and/or the elevation angle, depending on theorientation and shape of the receive antennas. When multiple antennasare used, the range-Doppler arrays for the antennas are averaged (e.g.,non-coherently summed) together to increase accuracy.

The FMCW radar system 100 is thus capable of measuring the range(distance from the radar), velocity (relative velocity with respect tothe radar) and angle of objects (with two or more transmit and/orreceive antennas) in the field of view of the radar. As explained above,the FMCW radar system 100 is configured to operate in either detectionmode or classification mode or, in some examples, standby mode.

FIG. 3a shows a frame 300 of the FMCW radar system 100 operating indetection mode, where the FMCW radar system 100 detects the start of anintended gesture. In the frame 300, the time between chirps (T_(chirp))is relatively long, since the maximum detectable velocity is not apriority when gesture classification is not being performed. Further, inthe frame 300, the chirps are generated by a single transmit antenna,since angle resolution is not a priority when gesture classification isnot being performed. By increasing T_(chirp) and transmitting only usinga single antenna, power consumption is reduced during detection mode.Additionally, in detection mode, additional power may be saved by usingonly a single receive antenna.

During detection mode, certain attributes of operation of the FMCW radarsystem 100 remain the same or approximately the same as duringclassification mode, which allows the FMCW radar system 100 toaccurately detect the start of an intended gesture, while stillbenefitting from the reduced power consumption explained above. Forexample, the duration of the frame 300 (T_(frame)) remains relativelylong (e.g., the same as T_(frame) in classification mode), allowing forgood velocity resolution. Similarly, the bandwidth of each chirp (B)remains relatively large (e.g., the same as B in classification mode),allowing for good range resolution. Further, the inter-frame idle time(not shown for brevity) remains sufficiently short (e.g., the same as inclassification mode), allowing for a high update or sample rate tocapture the relevant dynamics of a fast-moving gesture, which enables amore rapid transition from detection mode to classification mode.

In examples where the FMCW radar system 100 is configured to operate instandby mode, certain attributes of operation of the FMCW radar system100 remain the same or approximately the same as during detection mode,except that the inter-frame idle time may be increased, further reducingpower consumption. Although the FMCW radar system 100 has a slowerresponse time in standby mode than in detection mode, owing to theincreased inter-frame idle time, a user is still able to perform certainpositional cues (e.g., placing their hand in front of the FMCW radarsystem 100 for a certain amount of time) which allows the FMCW radarsystem 100 to accurately detect the user's intention to begin gesturing,while benefitting from additional reduced power consumption.

FIG. 3b shows a frame 350 of the FMCW radar system 100 operating inclassification mode, where the FMCW radar system 100 classifies one ormore gestures based on features extracted from the received radarsignals. In the frame 350, T_(chirp) is shortened relative to detectionmode above, which allows for an increased maximum detectable velocity toassist in classifying the one or more gestures. Further, in the frame350, the chirps are generated by multiple transmit antennas in aninterleaved manner, allowing for enhanced angle resolution. For example,the chirps 352, 356 are generated by a first transmit antenna while thechirps 354, 358 are generated by a second transmit antenna. In certainexamples, additional transmit antennas such as a third transmit antennamay be utilized to further improve the angle resolution of FMCW radarsystem 100. Additionally, in classification mode, multiple receiveantennas may be utilized to improve the angle resolution of the FMCWradar system 100.

Gestures may be classified based on an analysis of the range-Dopplerarrays 200 over time. For example, gestures may be classified based onthe velocity component of the range-Doppler array 200, where a positivevelocity peak indicates an object (e.g., a user's hand) is moving towardthe FMCW radar system 100 and a negative velocity peak indicates theobject is moving away from the FMCW radar system 100. As a furtherexample, a range-Doppler array 200 in which a positive velocity peaktransitions quickly to a negative velocity peak may indicate a wavingmotion. In other examples, angle detection allows for determination ofrotational movements, such as moving a finger or a hand in a circularmotion. Additional types of gesture classification may be based on, forexample, distance, velocity, and angle information of one or moredetected objects.

The DSP 118 or another processor is configured to compute a motionmetric based on the digital IF signals, to determine whether the FMCWradar system 100 operates in detection mode or classification mode. FIG.4a shows a flow chart of a method 400 of operating the FMCW radar system100 in accordance with examples of the present disclosure. The method400 begins in block 402 in detection mode, with the FMCW radar system100 transmitting frames as shown in FIG. 3a and computing the motionmetric for each frame. The method 400 continues in block 404, in whichthe motion metric is compared to a threshold, which may be determinedexperimentally, for example based on an intended use case or anenvironment for a given FMCW radar system 100. If the motion metric isbelow the threshold, the method 400 returns to block 402 and the FMCWradar system 100 continues to operate in detection mode.

However, if the motion metric is above the threshold, the method 400continues to block 406 and the FMCW radar system 100 entersclassification mode. When the FMCW radar system 100 operates inclassification mode in block 406, the FMCW radar system 100 transmitsframes as shown in FIG. 3b , and extracts features from the digital IFsignals (e.g., after 2D FFT processing) to perform gestureclassification. The method 400 continues in block 408, in which themotion metric is compared to the threshold. If the motion metric isabove the threshold (or falls below the threshold for less than apredetermined amount of time, P consecutive frames for example), themethod 400 returns to block 406, and the FMCW radar system 100 continuesto operate in classification mode. On the other hand, if the motionmetric falls below the threshold for at least P consecutive frames, themethod 400 returns to block 402, and the FMCW radar system 100 returnsto operate in detection mode, reducing the power consumption of thesystem when a gesture is not being performed (e.g., as indicated by themotion metric).

FIG. 4b shows a flow chart of another method 450 of operating the FMCWradar system 100, which includes a standby mode in accordance withexamples of the present disclosure. The method 450 begins in block 452in standby mode with the FMCW radar system 100 transmitting frames asshown in FIG. 3a , but with an increased inter-frame idle time toprioritize reduced power consumption. While in standby mode in block452, the method 450 also includes computing the motion metric for eachframe. The method 450 continues in block 454 in which the motion metricis compared to a threshold. If the motion metric is below the threshold,the method 450 returns to block 452 and the FMCW radar system 100continues to operate in standby mode.

However, if the motion metric is above the threshold, the method 450continues to block 462, and the FMCW radar system 100 entersclassification mode. When the FMCW radar system 100 operates inclassification mode as in block 462, the FMCW radar system 100 transmitsframes as shown in FIG. 3b and extracts features from the digital IFsignals (e.g., after 2D FFT processing) to perform gestureclassification. The method 450 continues in block 464, in which themotion metric is compared to the threshold. If the motion metric isabove the threshold (or falls below the threshold for less than apredetermined amount of time, P consecutive frames for example), themethod 450 returns to block 462 and the FMCW radar system 100 continuesto operate in classification mode.

On the other hand, if the motion metric falls below the threshold for atleast P consecutive frames, the method 450 continues to block 456, andthe FMCW radar system 100 enters detection mode, reducing the powerconsumption of the system relative to classification mode when a gestureis not being performed (e.g., as indicated by the motion metric). Indetection mode in block 456, the FMCW radar system 100 transmits framesas shown in FIG. 3a and computes the motion metric for each frame. Themethod 450 continues in block 458 in which the motion metric is comparedto the threshold. If the motion metric is above the threshold, themethod 450 continues to block 462 and the FMCW radar system 100 entersclassification mode, with the method 450 continuing as explained above.If the motion metric is below the threshold, the method 450 continues toblock 460, where it is determined if the motion metric is below thethreshold for a predetermined amount of time, Q consecutive frames inthis example. If the motion metric is not below the threshold for atleast Q consecutive frames, then the method 450 returns to block 456 andthe FMCW radar system 100 continues to operate in detection mode, withthe method 450 continuing as explained above. If the motion metric isbelow the threshold for at least Q consecutive frames, then the method450 returns to block 452 and the FMCW radar system 100 enters standbymode, with the method 450 continuing as explained above.

In the method 450, Q may be greater than P, such that a device inclassification mode (block 462, 464) switches to detection mode (block456) after a period of P consecutive frames of “no gestures,” or wherethe motion metric is below the threshold. Similarly, a device indetection mode (block 456, 458, 460) switches to standby mode after aperiod of Q consecutive frames of “no gestures,” or where the motionmetric is below the threshold. In at least one example, P consecutiveframes may correspond to approximately a few to tens of seconds, while Qconsecutive frames may correspond to a minute or more.

FIG. 5 shows an example of computing the motion metric, including arange-Doppler array 500, similar to the array 200 described above withrespect to FIG. 2 except viewed from above. The range-Doppler array 500includes regions 502, 504, which are a subset of the range-Doppler array500. The DSP 118 or other processor may compute the motion metric bycomputing a total energy (e.g., by integrating the distribution shown inFIG. 2) in the regions 502, 504 of the range-Doppler array.

In some examples, the regions 502, 504 are bounded in order to restrictthe motion metric computation to only moving objects (i.e., having anon-zero velocity, or a velocity greater than a minimum velocitythreshold). This avoids stationary objects in view of the radar system100 from contributing to the motion metric, possibly erroneously causinga switch to classification mode despite no gesture being performed.

Similarly, in some examples, the regions 502, 504 are bounded in orderto restrict the motion metric computation only to objects closer to theradar system or having a range less than a maximum distance threshold.This avoids background objects/movement in view of the radar system 100from contributing to the motion metric, possibly erroneously causing aswitch to classification mode even though the movement detected wasmerely background movement (e.g., in a large room where the radar systemis part of a thermostat).

FIG. 6 shows a block diagram of an example FMCW radar system configuredto support gesture recognition and switch between detection mode andoperation mode, as explained above. The radar system includes aprocessing unit 650 and an FMCW radar system-on-a-chip (SOC) 600. Insome examples, the processing unit 650 is integrated into the FMCW radarSOC 600. The radar SOC 600 may include multiple transmit channels 604for transmitting FMCW signals and multiple receive channels 602 forreceiving the reflected transmitted signals. Further, the number ofreceive channels may be larger than the number of transmit channels. Forexample, the radar SOC 600 may have two transmit channels and fourreceive channels. A transmit channel includes a suitable transmitter andantenna. A receive channel includes a suitable receiver and antenna.Further, each of the receive channels 602 are identical and include amixer 606, 608 to mix the transmitted signal with the received signal togenerate a beat signal (alternatively referred to as a dechirped signal,intermediate frequency (IF) signal, or raw radar signal), a basebandbandpass filter 610, 612 for filtering the beat signal, a variable gainamplifier (VGA) 614, 616 for amplifying the filtered beat signal, and ananalog-to-digital converter (ADC) 618, 620 for converting the analogbeat signal to a digital beat signal.

The receive channels 602 are coupled to a digital front end (DFE) 622that performs decimation filtering on the digital beat signals to reducethe sampling rate and bring the signal back to baseband. The DFE 622 mayalso perform other operations on the digital beat signals, e.g., directcurrent (DC) offset removal. The DFE 622 is coupled to high speedinterface component 624 to transfer the output of the DFE 622 to theprocessing unit 650.

The processing unit 650 may perform all or portions of the method ofoperating the radar system of FIG. 4 on the received digital beatsignals. The processing unit 650 may include any suitable processor orcombination of processors 651. For example, the processing unit 650 maybe a digital signal processor, a microcontroller unit (MCU), an FFTengine, a DSP+MCU processor, a field programmable gate array (FPGA), oran application specific integrated circuit (ASIC). As explained above,in certain examples, the processing unit 650 and/or the memory component652 are integrated into the FMCW radar SOC 600.

The memory component 652 provides storage, e.g., a non-transitorycomputer readable medium, which may be used, for example, to storesoftware instructions executed by processing unit 650, such as anysoftware instructions for implementing gesture recognition and switchingbetween detection mode and operation mode as explained above. The memorycomponent 652 may also store dechirped ADC data, range-Doppler arrays,and other data useful for computing the motion metric described above.The memory component 652 may include any suitable combination ofread-only memory (ROM) and/or random access memory (RAM), e.g., staticRAM.

The control component 626 includes functionality to control theoperation of the radar SOC 600. The control component 626 may include,for example, an MCU that executes software to control the operation ofthe radar SOC 600 between detection mode and operation mode.

The serial peripheral interface (SPI) 628 provides an interface forcommunication with the processing unit 650. For example, the processingunit 650 may use the SPI 628 to send control information, e.g., timingand frequencies of chirps, enabling of and timing between transmitantennas, output power level, triggering of monitoring functions, etc.,to the radar SOC 600.

The programmable timing engine 642 includes functionality to receivechirp parameter values for a sequence of chirps in a radar frame fromthe control component 626 and to generate chirp control signals thatcontrol the transmission and reception of the chirps in a frame based onthe parameter values, including timing between chirps generated bydifferent transmit antennas in classification mode, and between chirpsgenerated by the same transmit antenna in detection mode.

The radio frequency synthesizer (RFSYNTH) 630 includes functionality togenerate FMCW signals for transmission based on chirp control signalsfrom the timing engine 642. In some examples, the RFSYNTH 630 includes aphase locked loop (PLL) with a voltage controlled oscillator (VCO).

The clock multiplier 640 increases the frequency of the transmissionsignal from the RFSYNTH 630 to the frequency of the mixers 606, 608. Theclean-up PLL (phase locked loop) 634 operates to increase the frequencyof the signal of an external low frequency reference clock (not shown)to the frequency of the RFSYNTH 630 and to filter the reference clockphase noise out of the clock signal.

In the foregoing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other devices and connections. Similarly, adevice that is coupled between a first component or location and asecond component or location may be through a direct connection orthrough an indirect connection via other devices and connections. Anelement or feature that is “configured to” perform a task or functionmay be configured (e.g., programmed or structurally designed) at a timeof manufacturing by a manufacturer to perform the function and/or may beconfigurable (or re-configurable) by a user after manufacturing toperform the function and/or other additional or alternative functions.The configuring may be through firmware and/or software programming ofthe device, through a construction and/or layout of hardware componentsand interconnections of the device, or a combination thereof.Additionally, uses of the phrases “ground” or similar in the foregoingdiscussion are intended to include a chassis ground, an Earth ground, afloating ground, a virtual ground, a digital ground, a common ground,and/or any other form of ground connection applicable to, or suitablefor, the teachings of the present disclosure. Unless otherwise stated,“about,” “approximately,” or “substantially” preceding a valuemeans+/−10 percent of the stated value.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present disclosure. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A method comprising: operating in a first mode,wherein the operating in the first mode includes: causing a first subsetof a set of transmit antennas to provide a first set of frequencymodulated continuous wave (FMCW) chirps; receiving a first set ofreceived signals in response to the first set of FMCW chirps; anddetermining a motion metric of an object based on the first set ofreceived signals; operating in a second mode, wherein the operating inthe second mode includes: causing a second subset of the set of transmitantennas to provide a second set of FMCW chirps, wherein a number ofantennas in the second subset is greater than a number of antennas inthe first subset; receiving a second set of received signals in responseto the second set of FMCW chirps; and determining the motion metricbased on the second set of received signals; and determining whether tooperate in the first mode or the second mode based on the motion metric.2. The method of claim 1, wherein a time between chirps of the first setof FMCW chirps is greater than a time between chirps of the second setof FMCW chirps.
 3. The method of claim 1, wherein the operating in thesecond mode includes performing gesture classification.
 4. The method ofclaim 1, wherein: the receiving of the first set of received signals isvia a first set of receive antennas; the receiving of the second set ofreceived signals is via a second set of receive antennas; and a numberof antennas in the second set of receive antennas is greater than anumber of antennas in the first set of receive antennas.
 5. The methodof claim 1, wherein the determining of the motion metric in the firstmode includes: performing a two-dimensional (2D) fast Fourier transform(FFT) on the first set of received signals to generate a firstrange-Doppler array; computing a first total energy in a subset of thefirst range-Doppler array; and determining the motion metric based onthe first total energy.
 6. The method of claim 5, wherein the subset ofthe first range-Doppler array comprises bins of the first range-Dopplerarray having a velocity greater than a minimum velocity threshold. 7.The method of claim 5, wherein the subset of the first range-Dopplerarray comprises bins of the first range-Doppler array having a rangeless than a maximum distance threshold.
 8. The method of claim 5,wherein the subset of the first range-Doppler array comprises bins ofthe first range-Doppler array having a velocity greater than a minimumvelocity threshold and a range less than a maximum distance threshold.9. The method of claim 5, wherein the determining of the motion metricin the second mode includes: performing a 2D FFT on the second set ofreceived signals to generate a second range-Doppler array; computing asecond total energy in a subset of the second range-Doppler array; anddetermining the motion metric based on the second total energy.
 10. Themethod of claim 1 further comprising: operating in a third mode, whereinthe operating in the third mode includes: providing a third set of FMCWchirps, wherein a time between chirps of the third set of FMCW chirps isgreater than a time between chirps of the first set of FMCW chirps;receiving a third set of received signals in response to the third setof FMCW chirps; and determining the motion metric based on the third setof received signals.
 11. The method of claim 10, wherein the providingof the third set of FMCW chirps uses the first subset of the set oftransmit antennas.
 12. A system comprising: a set of transmit antennas;a set of receive antennas; and a processor coupled to the set oftransmit antennas and to the set of receive antenna and configured to:operate in a first mode by: causing a first subset of the set oftransmit antennas to provide a first set of frequency modulatedcontinuous wave (FMCW) chirps; receiving, via a first subset of the setof receive antennas, a first set of received signals in response to thefirst set of FMCW chirps; and determining a motion metric based on thefirst set of received signals; operate in a second mode by: causing asecond subset of the set of transmit antennas to provide a second set ofFMCW chirps, wherein a number of antennas in the second subset of theset of transmit antennas is greater than a number of antennas in thefirst subset of the set of transmit antennas; receiving, via a secondsubset of the set of receive antennas, a second set of received signalsin response to the second set of FMCW chirps; and determining the motionmetric based on the second set of received signals; and determinewhether to operate in the first mode or the second mode based on themotion metric.
 13. The system of claim 12, wherein a time between chirpsof the first set of FMCW chirps is greater than a time between chirps ofthe second set of FMCW chirps.
 14. The system of claim 12, wherein theprocessor is configured to operate in the second mode by furtherperforming gesture classification.
 15. The system of claim 12, wherein anumber of antennas in the second subset of the set of receive antennasis greater than a number of antennas in the first subset of the set ofreceive antennas.
 16. The system of claim 12, wherein the determining ofthe motion metric in the first mode includes: performing atwo-dimensional (2D) fast Fourier transform (FFT) on the first set ofreceived signals to generate a first range-Doppler array; computing afirst total energy in a subset of the first range-Doppler array; anddetermining the motion metric based on the first total energy.
 17. Thesystem of claim 16, wherein the subset of the first range-Doppler arraycomprises bins of the first range-Doppler array having a velocitygreater than a minimum velocity threshold and a range less than amaximum distance threshold.
 18. The system of claim 16, wherein thedetermining of the motion metric in the second mode includes: performinga 2D FFT on the second set of received signals to generate a secondrange-Doppler array; computing a second total energy in a subset of thesecond range-Doppler array; and determining the motion metric based onthe second total energy.
 19. The system of claim 16, wherein theprocessor is further configured to: operate in a third mode by: causinga third subset of the set of transmit antennas to provide a third set ofFMCW chirps, wherein a time between chirps of the third set of FMCWchirps is greater than a time between chirps of the first set of FMCWchirps; receiving, via a third subset of the set of receive antennas athird set of received signals in response to the third set of FMCWchirps; and determining the motion metric based on the third set ofreceived signals.
 20. The system of claim 19, wherein the first subsetof the set of transmit antennas and the third subset of the set oftransmit antennas is the same.